1. Field of the Invention
The present invention relates to a method of controlling power consumption for a radio receiver.
2. Description of the Related Art
For a radio that is limited in power usage such as a radio attached to a cellular phone or a laptop computer, various countermeasures are taken to reduce the power consumption. In a baseband unit of a radio receiver, the power consumption in a logic circuit is reduced due to the benefits of miniaturization and voltage reduction; however, an analog/digital converting unit (ADC) that is an analog circuit used to interface with a radio frequency unit cannot get the above benefits and therefore remains as a target for power reduction.
The power reduction of the ADC can be achieved by controlling a bias current. Therefore, in the present invention, it is considered to control the bias current of the ADC as a countermeasure for further reducing the power consumption of the radio receiver.
In this case, in a packet communication system, a modulation scheme is different for each packet in some cases. Moreover, even in a communication system in which a plurality of data is transmitted in one frame, the modulation scheme is different for each data in some cases. In this case, performance required for the ADC in the radio receiver is different depending on the modulation scheme. For example, a signal to noise ratio (SNR) required for the ADC is different between when receiving a signal modulated using 64 Quadrature Amplitude Modulation (QAM) and when receiving a signal modulated using Binary Phase Shift Keying (BPSK).
However, the performance of the ADC such as the SNR and a dynamic range changes along with the control of the bias current in the ADC, so that a problem arises in that the reception performance is degraded when applying to the radio receiver.
A technology for controlling the bias voltage of the ADC is disclosed, for example, in Japanese Patent Application Laid-open No. 2008-72742.